The present invention relates to methods and systems to achieve high-resolution overlay alignment for imprint lithography processes.
Imprint lithography is a technique that is capable of printing features that are smaller than 50 nm in size on a substrate. Imprint lithography may have the potential to replace photolithography as the choice for semiconductor manufacturing in the sub-100 nm regime. Several imprint lithography processes have been introduced during 1990s. However, most of them have limitations that preclude them from use as a practical substitute for photolithography. The limitations of these prior techniques include, for example, high temperature variations, the need for high pressures and the usage of flexible templates.
Recently, imprint lithography processes may be used to transfer high resolution patterns from a quartz template onto substrate surfaces at room temperature and with the use of low pressures. In the Step and Flash Imprint Lithography (SFIL) process, a rigid quartz template is brought into indirect contact with the substrate surface in the presence of light curable liquid material. The liquid material is cured by the application of light and the pattern of the template is imprinted into the cured liquid.
Using a rigid and transparent template makes it possible to implement high resolution overlay as part of the SFIL process. Also the use of a low viscosity liquid material that can be processed by light curing at low pressures and room temperatures lead to minimal undesirable layer distortions. Such distortions can make overlay alignment very difficult to implement.
Overlay alignment schemes typically include measurement of alignment errors between a template and the substrate, followed by compensation of these errors to achieve accurate alignment. The measurement techniques that are used in proximity lithography, x-ray lithography, and photolithography (such as laser interferometry, capacitance sensing, automated image processing of overlay marks on the mask and substrate, etc) may be adapted for the imprint lithography process with appropriate modifications. The compensation techniques have to be developed keeping in mind the specific aspects of imprint lithography processes.
Overlay errors that typically need to be compensated for include placement errors, theta error and magnification error. Overlay measurement techniques have been significantly improved during recent years as the minimum line width of photolithography processes have continued to shrink. However, these techniques may not be directly applicable to the imprint lithography processes.